There is known a vehicular drive system including a first electric motor, a differential portion, a second electric motor, and a transmission portion. JP-2003-301731A discloses an example of such a drive system for use on a hybrid vehicle. In the hybrid vehicle drive system disclosed in this publication, the first electric motor, differential portion, second electric motor and transmission portion are disposed coaxially with each other, such that they are arranged in the axial direction of the drive system in the order of description. Accordingly, the required axial dimension and width dimension of this vehicular drive system tend to be large. In particular, where the vehicular drive system is transversely installed on an FF (front-engine front-drive) vehicle or an RR (rear-engine rear drive) vehicle, this transverse installation of the drive system is difficult due to a limited space available for installation of the drive system on the FF or RR vehicle. For example, the drive system including the transmission portion as described above is installed on a hybrid vehicle known as “PRIUS” (registered trademark), an extensive analysis is required regarding the layout of the components of the drive system, so that the drive system can be installed within the limited width dimension of the hybrid vehicle. It is also noted that among an increased number of components of the drive system, the electric motors and the transmission portion that are assembled together have a relatively large number of restrictions in the assembling, the overall efficiency of assembling of the drive system tends to be considerably lowered. Thus, there has been a need for providing a vehicular drive system which has a reduced axial dimension and an improved accuracy of assembling.
It is considered to provide a vehicular drive system which has a plurality of parallel axes and in which the first electric motor, differential portion, second electric motor and transmission portion are arranged in a plurality of power transmitting paths on the respective parallel axes. However, no techniques have been available for adequately laying out the components of this type of vehicular drive system, which components include a housing structure consisting of separate housing portions. An inadequate layout of the components on the plurality of parallel axes does not permit sufficient reduction of the axial dimension of the drive system, and has a risk of deterioration of accuracy of support of various rotary members of the drive system.